Heat exchanger having sloped deflection surface for directing refrigerant

ABSTRACT

A heat exchanger such as an evaporator for a temperature control system includes an input port with an orifice through which a refrigerant enters the heat exchanger. The heat exchanger includes a plurality of plates and a tilted deflection surface near the input port. High-pressure refrigerant entering through the input port impinges on the tilted deflection surface and is deflected by the deflection surface onto the plates. The tilt angle of the deflection surface is selected such that the refrigerant is evenly distributed over the plates resulting in even and highly efficient heat transfer. The heat exchanger can be used as the evaporator in a refrigeration system used to control temperature in a workpiece chuck for supporting a flat workpiece such as a semiconductor wafer during processing and testing. In particular, the heat exchanger can be used to control the temperature of a fluid which is circulated through the chuck to control the temperature of the workpiece and/or the chuck itself. In that setting, the temperature control circulating fluid can be circulated through the heat exchanger over the sides of the plates opposite the refrigerant to cool the circulating fluid. Because the refrigerant is evenly distributed over the plates, highly efficient heat transfer, i.e., cooling, is achieved.

RELATED APPLICATIONS

This application is a continuation-in-part of copending U.S. application Ser. No. 09/001,887, filed on Dec. 31, 1997.

FIELD OF THE INVENTION

The present invention relates generally to power and control systems and more specifically to power and control systems used to control the temperature of a workpiece such as a semiconductor wafer and/or to control the temperature of the workpiece chuck on which the workpiece is held.

BACKGROUND OF THE INVENTION

In the semiconductor integrated circuit industry, the cost of individual integrated circuit chip die is continuing to decrease in comparison to IC package costs. Consequently, it is becoming more important to perform many IC process steps while the die are still in the wafer, rather than after the relatively expensive packaging steps have been performed.

Typically, in IC processing, semiconductor wafers are subjected to a series of test and evaluation steps. For each step, the wafer is held in a stationary position at a process station where the process is performed. For example, circuit probe testing is increasingly performed over a wide temperature range to temperature screen the ICs before assembly into a package. The wafer is typically held stationary relative to a vacuum support surface of a prober machine which electrically tests the circuits on the wafer. The prober includes a group of electrical probes which, in conjunction with a tester, apply predetermined electrical excitations to various predetermined portions of the circuits on the wafer and sense the circuits' responses to the excitations.

In a typical prober system, the wafer is mounted on the top surface of a wafer chuck, which is held at its bottom surface to a support structure of the prober. A vacuum system is typically connected to the chuck. A series of channels or void regions in communication with the top surface of the chuck conduct the vacuum to the wafer to hold it in place on the top surface of the chuck. The prober support structure for the chuck is then used to locate the wafer under the probes as required to perform the electrical testing on the wafer circuits.

The chuck can also include a temperature control system which raises and lowers the temperature of the chuck surface and the wafer as required to perform the desired temperature screening of the wafer. It is important to the accuracy of such testing that the temperature of the wafer and, therefore, the temperature of the chuck surface, be controlled as accurately and precisely as possible.

Various approaches to controlling the wafer temperature have been employed. In one prior system, the chuck includes a circulation system through which a cooling fluid is circulated. The cooling fluid is maintained at a constant cold temperature and is circulated through the chuck. Temperature control is realized by activating a heater which is also located in the chuck. The heater is cycled on and off as required to heat the chuck and the workpiece to the required temperature.

In another prior system, both a temperature-controlled fluid and a chuck heater are used to control the workpiece temperature. In this system, the fluid is used to bring the workpiece to within a certain tolerance of the desired set point temperature. The heater is then cycled as required to trim the temperature to the set point.

Temperature control systems can typically include heat exchangers such as condensers and evaporators for heating and cooling a medium such as circulated air or liquid. For example, in an air conditioning system, a refrigerant such as freon is circulated through the system to remove heat from circulated air. Specifically, the evaporator heat exchanger is in close proximity to the air to be cooled. As the freon evaporates, it removes heat from the air to cool the air.

In one type of conventional evaporator, the cold refrigerant enters the evaporator through an orifice and is allowed to flow over metal plates arranged parallel to each other with spaces between them for the refrigerant. As the refrigerant flows between the plates, the plates cool. In one configuration, the cooled medium, e.g., air, is routed through the evaporator such that it also flows between the plates on the sides opposite the sides in contact with the refrigerant, and the air is cooled by the cold plates.

In many settings, it is important that the evaporator be extremely efficient and provide as much cooling as possible. For example, in a workpiece chuck in which a circulating fluid is used in controlling workpiece and/or chuck temperature, it is important that the workpiece and/or chuck be heated and cooled very quickly and with a high degree of accuracy. In such a case, the evaporator should have very high efficiency. The efficiency of the evaporator can be affected by many factors. For example, in conventional evaporators, the low-temperature refrigerant enters the evaporator through the orifice at high pressure. It is in general distributed over the plates in an uncontrolled and uneven fashion, which results in a loss in efficiency. It would be beneficial to have the refrigerant distributed evenly over the plates such that the plates are cooled evenly. This would provide even cooling of the circulating temperature controlling fluid and also provide the most cooling for a given set of system parameters.

SUMMARY OF THE INVENTION

In accordance with the invention, there is provided a highly efficient heat exchanger and temperature controlling method which overcome the drawbacks of the prior art. The heat exchanger of the invention includes an input port through which a refrigerant enters the heat exchanger as well as a plurality of plates which receive the refrigerant. A tilted deflection surface is located near the input port and is contacted by the refrigerant as it enters the heat exchanger. The tilted deflection surface directs the refrigerant such that the refrigerant is distributed over the plates. In one embodiment, the heat exchanger of the invention is an evaporator.

In one embodiment, the deflection surface is formed as part of an insert which is mounted inside the input port through which the refrigerant enters the heat exchanger. The input port can include an orifice though which the refrigerant enters the heat exchanger. In one embodiment, the orifice is formed as part of the insert mounted in the input port. The tilt angle of the deflection surface is selected such that the refrigerant is evenly distributed over the plates, resulting in uniform efficient cooling in the evaporator.

The heat exchanger of the invention is mounted such that the cold refrigerant enters the heat exchanger at the top of the device. The refrigerant flows over the plates to the bottom of the device where it exits the device through an output. In many settings, the refrigerant flowing through the evaporator is accompanied by a lubricant used by other devices in the refrigeration cycle, such as a compressor. Because the refrigerant and lubricant flow from the top to the bottom of the evaporator, the lubricant simply flows out of the device by gravity and need not be recovered by such means as a capillary tube, as used in prior devices.

In one embodiment, the heat exchanger, e.g., evaporator, of the invention is used in a temperature control system which operates to control the temperature of a circulating fluid. For example, in one embodiment, the fluid is circulated through a workpiece chuck in which the temperature of a workpiece, such as a semiconductor wafer, can be controlled. The temperature of the fluid is controlled by the temperature control system that uses the heat exchanger of the invention. In such a system, the heat exchanger of the invention includes a fluid input and a fluid output such that the temperature control fluid can be circulated through the device. The fluid runs through the device through the plates which are cooled by the refrigerant. Heat is therefore removed from the fluid and transferred to the refrigerant via the plates. In one particular embodiment, the circulating temperature control fluid comprises methyl nonafluoroisobutyl ether. In an alternative embodiment, the fluid comprises methyl nonafluorobutyl ether.

The heat exchanger of the present invention can be used in many temperature control settings. In particular, the heat exchanger of the invention can be the evaporator in a fluid temperature control system used to control temperature in a workpiece chuck by controlling the temperature of a fluid circulated through the chuck. Such a system is described in, for example, copending U.S. patent application Ser. No. 09/001,887, filed on Dec. 31, 1997, of the same assignee as the assignee of the present application. The contents of that application are incorporated herein by reference.

The present invention provides numerous advantages over conventional heat exchangers, in particular, evaporators. The tilted deflection surface is used to evenly distribute the refrigerant over the evaporator plates. As a result, more uniform cooling of the plates is achieved. This results in more efficient heat transfer from the circulating temperature control fluid and more efficient overall operation of the host temperature control system.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawing. The drawing is not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

FIG. 1 is a schematic detailed block diagram of one embodiment of the temperature control system of the invention.

FIG. 2 is a schematic detailed block diagram of an alternative embodiment of the temperature control system of the invention.

FIG. 3 contains a schematic perspective view of an evaporator in accordance with one embodiment of the present invention.

FIG. 4 is a schematic cross-sectional diagram of the interior of the evaporator of FIG. 3 in accordance with the invention.

FIGS. 5A and 5B contain schematic cross-sectional views of one embodiment of the distribution manifold in accordance with the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 is a schematic diagram of one particular temperature control system 100 in which the heat exchanger and temperature control method in accordance with the present invention can be used. The temperature control system in the example of FIG. 1 is used in connection with a workpiece chuck 10. The chuck 10 can be used to hold on its top surface 12 a flat workpiece such as a semiconductor wafer during processing and can be of the form described in a copending patent application entitled “Workpiece Chuck,” filed on Dec. 31, 1997, assigned to the same assignee as the present application, and incorporated herein in its entirety by reference.

The processing performed on the workpiece can include electrical circuit testing on a wafer over a predetermined range of temperatures using a host machine such as a prober machine.. To implement temperature cycling of the wafer, the chuck 10 includes a heat sink 14 through which fluid can be circulated and an electrical heater 16 which can be used to heat the wafer. The temperature control system 100 of the invention is used to control the heater 16 and the temperature and flow of fluid through the heat sink 14 in order to control the temperature of the chuck and, therefore, the temperature of the wafer under test. As described in detail below, in one embodiment, the heater 16, also referred to herein as H3, can actually include two resistive heating elements 16A and 16B, each of which is powered by its own individually controllable power signal provided by the power and control system of the invention. The heating elements 16A and 16B are individually controllable to permit implementation of a multiple-stage, e.g., two-stage, workpiece heating procedure as described below in detail.

It should be noted that in FIG. 1 broken or dashed lines indicate electrical connections and solid lines with arrowheads indicate lines for implementing flow of a thermodynamic medium such as the fluid used for controlling the temperature of the chuck or the refrigerant used to cool that fluid.

The system 100 of the invention can also be used to maintain a lower portion of the chuck 10 at ambient environment temperature to prevent heat flow between the chuck 10 and the host machine. To that end, the chuck 10 includes a lower support or plate 22, which can be a ceramic thermal and electrical insulating plate, which is mounted to a base 48. In one embodiment, the base 48 is part of the host machine on which the chuck 10 is mounted. In another embodiment, as shown in FIG. 1, the base 48 is part of the chuck. The base will be referred to herein as being part of the chuck 10, but it will be understood that it can also be a part of the host machine. In either case, the temperature of the base 48 is controlled to control heat flow between the chuck 10 and the host machine. The fluid can be circulated through the base 48 to maintain the base at ambient temperature. This sets up a heat flow barrier between the chuck and the host machine.

The temperature control system 100 of the invention includes a fluid temperature control module 110 which controls the temperature and the flow of fluid to and from the chuck 10. The fluid is carried into the heat sink 14 via an inlet line 112 and out of the heat sink 14 via a return line 113. The fluid can also be carried into the base 48 via another inlet line 114 and out of the base 48 via another return line 115. The two return lines 113 and 115 join together into a single return line 116 which returns the fluid to the fluid control module 110. The fluid can be methyl nonafluoroisobutyl ether. Alternatively, the fluid can be methyl nonafluorobutyl ether

The system 100 of the invention also includes a power and control system which can include an electrical controller 50 and a power supply 60. The controller 50 receives electrical input signals from various components of the system 100 and transmits electrical control signals to system components as required to perform the required temperature control functions of the system 110. The power supply 60 supplies power to the various system components and the controller 50 as required.

In one embodiment of the invention, temperature feedback is provided to the controller 50 by a series of temperature sensors located at various positions in the chuck 10 and the temperature control module 110. In the embodiment shown in FIG. 1, six temperature sensors, labeled T1-T6, are used. It should be noted that the references to T1-T6 contained herein can be to either the sensor itself or the temperature value it indicates. It will be clear from the context which is intended.

Sensor T1 is the chuck upper surface temperature sensor which indicates the chuck temperature at or near the heat sink 14. In one embodiment, before temperature testing, a calibration process is performed in which the difference between the temperature at sensor T1 and the actual temperature at the wafer is determined. During the calibration, temperature of the wafer at the top surface can be determined by a surface-mounted thermocouple or other temperature sensor, or by using a calibrated diode on the wafer, or by some other technique; and a correction factor is generated which identifies the temperature differential between sensor T1 and the wafer surface. That correction factor is used as an adjustment during subsequent temperature control processes to maintain the wafer at the desired temperature. Alternatively, a contact or non-contact temperature sensor can be used at the wafer surface to provide the T1 temperature measurement. This eliminates the need for the calibration. This temperature sensor can be a calibrated diode, a thermocouple or any other contact or non-contact sensor.

Sensor T2 is the base temperature sensor. It senses the temperature at the base 48. This temperature is maintained at or near ambient temperature (sensor T3) to prevent heat flow between the chuck 10 and the host machine. Sensor T3 is the ambient air/environment temperature sensor. It senses the ambient temperature of the environment around the chuck and the host machine. Ideally, by circulating fluid through the base 48, T2 is maintained as close as possible to T3 to prevent heat flow between the chuck and the host machine.

Sensor T4 is a fluid temperature sensor. It senses the temperature of the fluid as it flows out of the fluid heater H1 and before it flows to either the heat sink 14 via line 112 or the base 48 via fluid heater H2 and line 114, depending upon the state of valve SV4. The temperature at T4 is monitored to allow control of the fluid temperature as it enters the heat sink 14 or the base 48.

Sensor T5 is the base fluid temperature sensor. It senses the temperature of the fluid as it flows out of the fluid temperature control module 110 toward the chuck 10 along line 114. The temperature at T5 is monitored to allow control of the fluid temperature as it enters the base 48, such that the base temperature (T2) can be maintained near ambient temperature (T3).

Sensor T6 is the return fluid temperature sensor. It senses the temperature of the fluid as it returns from the chuck 10 along return line 116. It is used to determine whether thermodynamic processes such as pre-cool should be performed on the fluid before it is circulated back to the chuck 10.

It should be noted that other temperature sensor configurations can be used. For example, sensors T1 and T2 can be located in return tubes 113 and 115, or additional sensors can be added to either or both of tubes 113 and 115.

The temperature control system 100 also includes the pair of fluid heaters H1 and H2 for heating the circulating fluid as required. Heater H2, the base fluid temperature control heater, heats fluid that is directed through the base 48. Heater H1, the chuck/base fluid temperature control heater, heats fluid that can be circulated through either the heat sink 14 or the base 48, depending on the state of SV4. As mentioned above, the system 100 also includes the chuck temperature control heater 16 (H3), which is located in the chuck 10 to provide heat directly to the chuck 10 to heat the workpiece and which can actually include multiple individually controllable heating elements 16A and 16B.

The flow of fluid through the system 100 is controlled via the controller 50 by a pump 120 and a series of valves. The pump 120 receives the fluid from the evaporator 134 and/or its bypass and accumulator 154 and pumps the fluid toward the fluid heaters H1 and H2 and then to the heat sink 14 and/or base 48.

The condenser 130, evaporator 134, thermal expansion valve 136, compressor 140 and pressure regulator 138 are used to implement a capacity-controlled refrigeration cycle that cools the fluid as required. Under particular predetermined circumstances described below, solenoid valves SV2 and SV3 are used to route the fluid through the refrigeration system as required to remove heat from the fluid. Under other circumstances, SV2 and SV3 are used to route the fluid such that it bypasses one or more portions of the refrigeration cycle. The ambient pre-cooler select solenoid valve SV2 is used to route the fluid through the ambient pre-cool heat exchanger 135. When ambient pre-cool is desired, SV2 is switched to its ON state to route the fluid through the pre-cool heat exchanger 135. When SV2 is OFF, as shown in FIG. 1, the fluid bypasses ambient pre-cool.

When further cooling of the fluid is desired, the fluid can be routed through the evaporator 134. The evaporator bypass select solenoid valve SV3 and the evaporator bypass coolant fluid metering valve M2 are used to control the flow of fluid through the evaporator 134. The metering valve M2 always allows a predetermined percentage of the fluid in line 142 to bypass the solenoid valve SV3 and flow into the evaporator 134 for cooling. In one embodiment, this percentage is set to about 15%. When SV3 is in its OFF state as shown in FIG. 1, all of the fluid in line 142 is routed through the evaporator for cooling. When SV3 is ON, the predetermined percentage (15%) of fluid flows into the evaporator 134, and the remaining fluid bypasses the evaporator 134 and flows toward pump 120.

A predetermined amount of the fluid at the outlet of pump 120 flowing in line 144 flows into heater H1. This amount is set by the base supply fluid metering valve M3. In one embodiment, M3 is set to cause 5% of the fluid in line 144 to bypass H1 and flow toward H2 in line 145 and the remaining 95% to flow through H1. Thus, in this configuration, some portion of the fluid will always flow through the base 48, and the temperature of that portion is controllable.

Under certain conditions, such as when the chuck is being heated by the chuck heater(s) 16 (H3), the fluid out of heater H1 will be routed by the chuck heat sink bypass select solenoid valve SV4 to line 147 to flow through heater H2 and the base 48 instead of the heat sink 14. When SV4 is ON, all of the fluid out of both H1 and H2 flows through the base 48. When SV4 is OFF as shown, the fluid out of the heater H1 is routed through the heat sink 14.

The system 100 also incorporates a dewpoint sensor 150 and a dewpoint meter 152. The dewpoint sensor 150 detects the dewpoint in the ambient environment around the chuck 10 and generates and transmits an electrical signal indicative of the sensed dewpoint to the dewpoint meter 152. The dewpoint meter 152 can send a dewpoint alarm signal to the controller 50 by closing a switch if the dewpoint rises above a particular value. Corrective actions such as heating the chuck to ambient and shutting down the system can be taken to avoid damage to the workpiece due to environmental factors such as frost formation.

The accumulator 154 serves as a reservoir for the fluid circulated through the chuck 10. The accumulator holds enough fluid to accommodate expansion and contraction of the fluid over the wide operating temperature range of the system. A signal indicating a low fluid level is generated by the accumulator 154 and transmitted to the controller 50 on line 149.

The controller 50 can also receive inputs from the host machine, e.g., prober, via an RS-232 interface 237. The RS-232 interface allows the host machine to communicate to the chuck such information as new chuck temperature set points.

The control logic used by the temperature control system 100 will now be described in detail. Certain variables are defined in connection with the operation of the system 100. T_(C) is defined as the temperature set point for the chuck 10. It is the temperature to which it is presently desired to set the chuck. T_(EB) is the evaporator bypass switching temperature. It is a constant positive number to which T_(C) is compared under some conditions. T_(S) is the support plate or base temperature set point and is typically approximately equal to T3, the ambient air/environment temperature. DT_(C) is the chuck temperature deviation which is a measure of the difference between the chuck temperature T1 and the chuck temperature set point T_(C), i.e., DT_(C)=T1-T_(C).

DT_(S) is the maximum value of chuck temperature deviation for which the chuck is defined to be at steady state and is typically equal to a constant positive number between 1 and 5° C. The chuck temperature is considered to be at steady state when the magnitude of the difference between the actual temperature and the set point (DT_(C)) is small, that is, when the actual temperature is only slightly different from the desired temperature. Specifically, the chuck is considered to be at steady state when −DT_(S)<DT_(C) <DT_(S).

The system 100 controls temperature of the chuck and workpiece over a wide range of temperatures. In one embodiment, the temperature range is effectively divided into a lower subrange and an upper subrange. In the lower subrange, the temperature of the chuck 10 and workpiece are controlled by fluid flow through the chuck 10 only; the chuck heater 16 (H3) is not activated. This is true even when the temperature set point may be above ambient temperature. In that case, the fluid provides the required heating. In the upper subrange, the chuck heater 16 is used to heat the chuck 10 and workpiece. The temperature at the boundary between the lower subrange and the upper subrange will be referred to herein by T_(B). In one embodiment, T_(B)=+40° C. Hence, where the total temperature range is, for example, −10° C. to +200° C., the lower subrange can extend from −10° C. to +39.9° C., and the upper subrange can extend from +40° C. to +200° C. Other temperature subranges can also be selected.

To describe the logical operation of the system 100, the settings of the various components of the system 100 will be described along with the physical system conditions under which the settings are made. As mentioned above, the compressor 140 and condenser 130 are part of a refrigeration system which is controllable to control the temperature of the fluid circulated through the chuck 10 in accordance with the present invention. The compressor 140 and condenser fan are ON when the system 100 is in operation and OFF otherwise. The pump 120 used to circulate the fluid through the chuck 10 is also ON when the system 100 is in operation and OFF otherwise.

Valve SV2 will be turned ON to implement the ambient pre-cool by routing the fluid through the pre-cool heat exchanger 135 when it is desired to cool the chuck to a set point temperature that is far enough below the current actual chuck temperature T₁ to take the system out of steady state, i.e., DT_(C)>DT_(S), and the temperature T₁ is greater than T_(B). Otherwise, SV2 will be turned OFF to bypass the ambient pre-cool.

As described above, when solenoid valve SV3 is OFF as shown in FIG. 1, the fluid is routed through the evaporator 134 to cool the fluid. When SV3 is ON, most of the fluid is routed to heater H1 to heat the fluid. SV3 will be turned ON under either of two sets of conditions. It will be ON when it is desired to heat the chuck to a temperature that is high enough above the current actual chuck temperature to take the system out of steady state, i.e., DT_(C)<−DT_(S). Alternatively, SV3 will be ON when the system is in the steady state condition, i.e., −DT_(S)<DT_(C)<DT_(S), and it is desired to operate the system in the upper temperature subrange, i.e., T_(C)≧T_(B). Otherwise, SV3 will be turned OFF to cool the fluid.

As described above, solenoid valve SV4 controls whether the fluid out of heater H1 is routed to the heat sink 14 or the base 48. When SV4 is ON, the fluid is routed to the base 48; when SV4 is OFF, the fluid is routed to the heat sink 14. SV4 will be turned ON when it is desired to operate the system in the upper temperature subrange, i.e., when T_(C)>T_(B), except when it is desired to cool the chuck to a set point temperature that is far enough below the current actual chuck temperature to take the system out of steady state, i.e., when DT_(C)>DT_(S). Otherwise, SV4 will be ON.

The heaters H1, H2 and H3 can be controlled by proportional-integral-derivative (PID) control loops implemented in the controller 50. The various temperature sensors T1-T6 provide the required temperature feedback which allows the controller 50 to control the heaters. The controller 50 provides pulse-width modulated signals to cycle the heaters on and off as required.

Heater H1 is cycled ON via the PID control to maintain the chuck temperature T1 equal to the set point temperature T_(C) when it is desired to operate the system in the lower temperature subrange, i.e., when T_(C)<T_(B), except when it is desired to cool the chuck to a temperature that is far enough below the current actual chuck temperature to take the system out of steady state, i.e., when DT_(C)>DT_(S). Heater H1 is also cycled ON to maintain the support plate temperature T2 equal to the ambient air/environment temperature T3 when it is desired to operate the system in the upper temperature subrange, i.e., when T_(C)≧T_(B), except when it is desired to cool the chuck to a temperature that is far enough below the current actual chuck temperature to take the system out of steady state, i.e., when DT_(C)>DT_(S). Heater H1 is OFF under other conditions.

Heater H2 is cycled ON via the PID control to maintain the base temperature T2 equal to the ambient air/environment temperature T3 except when SV4 is turned ON to cause the fluid out of heater H1 to flow through the base 48. In this case, heater H1 handles the bulk of the heating load for the fluid. Under other circumstances, heater H2 is OFF.

The chuck heater H3 is cycled on via PID control to maintain the temperature of the chuck T1 equal to the set point temperature T_(C) when it is desired to operate the system in the upper temperature subrange, i.e., when T_(C)≧T_(B), except when it is desired to cool the chuck to a temperature that is far enough below the current actual chuck temperature to take the system out of steady state, i.e., when DT_(C)>DT_(S). Under other conditions, the heater H3 is OFF.

FIG. 2 is a schematic detailed block diagram of another temperature control system 400 in which the present invention can be used. The components and control logic described above in connection with FIG. 1 are the same as those of FIG. 2 with some exceptions as described below. The system 400 of FIG. 2 uses a different fluid temperature control system 410 than the system 100 described in connection with FIG. 1. The fluid refrigeration system of FIG. 2 includes a condenser 130 and an evaporator 434. The refrigerant used to cool the circulation fluid exits the condenser 130 along line 453 and enters an expansion valve 438 where it is throttled before it enters the evaporator 434. The solenoid valve SV2 can be used to bypass the ambient pre-cool heat exchanger 435 when further cooling of the chuck temperature control fluid is not desired. However, the solenoid valve SV3 of the system of FIG. 1, used to bypass the evaporator where further cooling is not required, is not included in the fluid temperature control system 410 of FIG. 2. Instead, when further cooling of the fluid is not desired, the normally closed solenoid valve SV6 is held closed to shut off cold refrigerant to the evaporator, and hot gas from the compressor is fed along line 451 into the evaporator 434 to provide heating of the fluid. In one configuration, when this extra heating is desired, the optional hot gas bypass enable solenoid valve SV5 is opened to allow the hot gas from the compressor 140 to be transmitted to the evaporator 434. A hot gas pressure regulator 436 is used to control the amount of hot gas introduced to the evaporator 434 according to the amount of heating required.

Hence, SV6 is used in controlling the fluid temperature by modulating refrigeration capacity at the evaporator heat exchanger 434. SV6 may be controlled through a controller PID loop to maintain fluid temperature as precisely as required.

In one configuration, another optional valve SV7 is included between the condenser 130 and evaporator 434. Valve SV7 feeds a fast response metering device which can be a capillary tube 439. SV7 can also be controlled through a PID loop. It differs from SV6 however in that it controls a lower capacity, faster responding metering device (capillary tube 439). Where this arrangement is used, SV6 can be energized for maximum capacity, during transitions for example. SV7 can then be used to maintain the set point precisely after transition while SV6 is de-energized.

Also, temperature sensor T6 in FIG. 1 is not used in the system of FIG. 2, and another temperature sensor T7 is added. Sensor T7 is the evaporator fluid outlet temperature sensor. It senses the temperature of the fluid as it leaves the evaporator heat exchanger 434. The sensed temperature at T7 is used to adjust the refrigeration capacity of the fluid refrigeration subsystem which includes condenser 130, compressor 140 and evaporator 434.

The power and control system used to control and operate the temperature control systems of FIGS. 1 and 2 can be of the type described in copending U.S. application Ser. No. 09/001,927, filed on Dec. 31, 1997, of the same assignee as the assignee of the present application. That application is incorporated herein in its entirety by reference.

In accordance with the present invention, the evaporators 134 and 434 in the temperature control systems of FIGS. 1 and 2, respectively, are extremely efficient. In the evaporator of the invention, the refrigerant flowing through the evaporator is distributed evenly over the internal plates such that even cooling of the plates is achieved.

FIG. 3 contains a schematic perspective view of a heat exchanger, e.g., evaporator 534, in accordance with one embodiment of the present invention, and FIG. 4 contains a schematic cross-sectional diagram of the interior of the evaporator 534 of FIG. 3 in accordance with the invention . The heat exchanger 534 of FIGS. 3 and 4 can be used as the evaporator 134 or 434 in the refrigeration systems shown in FIGS. 1 or 2, respectively. The evaporator 534 includes a refrigerant inlet 502 through which the system refrigerant enters the evaporator 534. The refrigerant passes through an orifice 503 and is distributed over vertically oriented heat exchange elements in the form of parallel plates 508. The refrigerant flows down in the spaces between the plates 508 to cool them and is collected at the bottom of the evaporator 534. It flows out of the evaporator 534 through the refrigerant outlet 510 and is cycled through the remainder of the refrigeration system.

In accordance with the invention, after the refrigerant passes through the orifice 503, it enters a distribution manifold 504 which is implemented in one embodiment as an insert in the inlet 502. The distribution manifold 504 is attached such as by threads, soldering, brazing or other method to the inside of the evaporator unit 534 at the refrigerant inlet 502. In one embodiment the distribution manifold is formed integrally with the orifice 503, that is, the distribution manifold 504 and orifice 503 are formed as a single unit with the orifice 503 serving as the input to the manifold 504. In one embodiment, the distribution manifold 504 and orifice 503 are formed from a single piece of metal, such as brass, by molding and/or machining.

Distribution manifold 504 includes a substantially flat, tilted deflection surface 506. Refrigerant under high pressure enters the manifold 504 from the orifice 503 and strikes the tilted deflection surface 506. The refrigerant impinges on the deflection surface 506 and flows or drips down into the spaces between the plates 508. Because of the tilt in the deflection surface, the refrigerant is evenly distributed across the plates 508 such that even and efficient cooling of the plates 508 is realized.

In many refrigeration systems which use evaporators and compressors, a lubricant is circulated through the refrigeration cycle along with the refrigerant in order to lubricate one or more components of the cycle, in particular the compressor. The refrigerant can separate from the lubricant. In conventional evaporators, the separated lubricant must be pumped out of the device and back into the refrigeration cycle. To effect this removal of lubricant, the conventional evaporator must be provided with a capillary tube in a reservoir area in which the lubricant collects. As shown in FIGS. 3 and 4, in one embodiment, the evaporator of the invention 534 is oriented such that the refrigerant and lubricant flow by gravity through the evaporator 534 over the plates 508 and out of the evaporator 534 at the bottom, without the need for a separate process and mechanism for removal of the lubricant. This adds considerable cost and efficiency savings to the evaporator of the invention.

As described above, the evaporator 534 of the invention is applicable in temperature control settings in which a circulating fluid is used to control temperature of a device such as a workpiece held on a workpiece chuck. To that end, the temperature control fluid can be circulated through the evaporator 534 to cool the fluid. The fluid enters the evaporator 534 through a fluid inlet 512 and flows through the evaporator 534 in channels 701 formed within the plates 508 and in tubes 703 connected between the plates 508. Heat is transferred from the temperature control fluid inside the plates to the refrigerant impinging on the outside surfaces of the plates to cool the fluid and heat the refrigerant. The cooled fluid exits the evaporator through the fluid outlet 514.

Thus, cold refrigerant enters the top of the evaporator 534 through the refrigerant inlet 502 and flows down along the plates 508 as it is warmed. The warmed refrigerant exits the evaporator 534 through the outlet 510 at the bottom. In contrast, the temperature control fluid in a relatively warm state enters the evaporator 534 at the bottom through the inlet 512 and flows up to the outlet 514. This arrangement provides for a highly efficient heat transfer since the circulating temperature control fluid travels toward the coldest refrigerant as it passes through the evaporator 534.

FIGS. 5A and 5B contain schematic cross-sectional views of the distribution manifold 504 in accordance with one embodiment of the invention. The drawings in FIGS. 5A and 5B are rotated with respect to each other ninety degrees about the longitudinal axis of the manifold 504. As shown in the figures, the manifold 504 in this embodiment includes the orifice 503 through which the refrigerant enters the evaporator 534. The manifold 504 also includes the tilted deflection surface 506 formed along the body of the manifold 504. As described above, the refrigerant enters the manifold 504 through the orifice 503 and is directed by the tilted deflection surface 506 such that the refrigerant is evenly distributed over the evaporator plates 508.

While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the following claims. 

What is claimed is:
 1. A heat exchanger for a temperature control system comprising: an input port through which a refrigerant enters the heat exchanger; a plurality plates; and a deflection surface near the input port for directing the refrigerant over the plates, the deflection surface being tilted such that the refrigerant is distributed over the plates, the deflection surface being formed as part of an insert mountable within the input port.
 2. The heat exchanger of claim 1, wherein the insert includes an orifice through which the refrigerant enters the heat exchanger.
 3. The heat exchanger of claim 1, wherein the input port includes an orifice through which the refrigerant enters the heat exchanger.
 4. The heat exchanger of claim 1 wherein an angle of tilt of the deflection surface is such that the refrigerant is distributed evenly over the plates.
 5. The heat exchanger of claim 1 wherein the heat exchanger is an evaporator.
 6. The heat exchanger of claim 1 further comprising an output through which the refrigerant exits the heat exchanger.
 7. The heat exchanger of claim 4 wherein the heat exchanger is oriented such that lubricant in the refrigerant exits the heat exchanger through the output with the refrigerant.
 8. The heat exchanger of claim 1 further comprising a fluid input for circulating a fluid through the heat exchanger, the fluid exchanging heat with the refrigerant.
 9. The heat exchanger of claim 8 wherein the fluid is cooled by the heat exchanger.
 10. The heat exchanger of claim 8 wherein the fluid comprises methyl nonafluoroisobutyl ether.
 11. The heat exchanger of claim 8 wherein the fluid comprises methyl nonafluorobutyl ether.
 12. The heat exchanger of claim 8 wherein the temperature control system is used to control temperature in a workpiece chuck used to support a workpiece.
 13. The heat exchanger of claim 12 wherein the workpiece is a semiconductor wafer.
 14. The heat exchanger of claim 12 wherein the fluid is circulated through the workpiece chuck to control temperature of the workpiece.
 15. The heat exchanger of claim 1 wherein the temperature control system is used to control temperature in a workpiece chuck used to support a workpiece.
 16. The heat exchanger of claim 15 wherein the workpiece is a semiconductor wafer.
 17. A method of controlling temperature comprising: allowing a refrigerant to enter a heat exchanger through an input port; and directing the refrigerant onto a tilted deflection surface within the heat exchanger such that the refrigerant is directed by the tilted deflection surface onto a plurality of plates in the heat exchanger, the deflection surface being formed as part of an insert mountable within the input port.
 18. The method of claim 17 wherein the insert is formed with an orifice through which the refrigerant enters the heat exchanger.
 19. The method of claim 17 wherein the input port includes an orifice through which the refrigerant enters the heat exchanger.
 20. The method of claim 17 wherein an angle of tilt of the deflection surface is such that the refrigerant is distributed evenly over the plates.
 21. The method of claim 17 wherein the heat exchanger is an evaporator.
 22. The method of claim 17 further comprising allowing the refrigerant to exit the heat exchanger through an output.
 23. The method of claim 22 further comprising orienting the heat exchanger such that lubricant in the refrigerant exits the heat exchanger through the output with the refrigerant.
 24. The method of claim 17 further comprising circulating a fluid through the heat exchanger, the fluid exchanging heat with the refrigerant.
 25. The method of claim 24 wherein the fluid is cooled by the heat exchanger.
 26. The method of claim 24 wherein the fluid comprises methyl nonafluoroisobutyl ether.
 27. The method of claim 24 wherein the fluid comprises methyl nonafluorobutyl ether.
 28. The method of claim 24 wherein the temperature is controlled in a workpiece chuck used to support a workpiece.
 29. The method of claim 28 wherein the workpiece is a semiconductor wafer.
 30. The method of claim 28 wherein the fluid is circulated through the workpiece chuck to control temperature of the workpiece.
 31. The method of claim 17 wherein the temperature is controlled in a workpiece chuck used to support a workpiece.
 32. The method of claim 31 wherein the workpiece is a semiconductor wafer.
 33. A temperature control system for a workpiece chuck, comprising: a pump for circulating a fluid in the workpiece chuck; and a refrigeration system for controlling temperature of the fluid, the refrigeration system including a heat exchanger, the heat exchanger comprising: an input port through which a refrigerant enters the heat exchanger, a plurality plates, and a deflection surface near the input port for directing the refrigerant over the plates, the deflection surface being tilted such that the refrigerant is distributed over the plates, the deflection surface being formed as part of an insert mountable within the input port.
 34. The temperature control system of claim 33, wherein the insert includes an orifice through which the refrigerant enters the heat exchanger.
 35. The temperature control system of claim 33, wherein the input port includes an orifice through which the refrigerant enters the heat exchanger.
 36. The temperature control system of claim 33 wherein an angle of tilt of the deflection surface is such that the refrigerant is distributed evenly over the plates.
 37. The temperature control system of claim 33 wherein the heat exchanger is an evaporator.
 38. The temperature control system of claim 33 further comprising an output through which the refrigerant exits the heat exchanger.
 39. The temperature control system of claim 38 wherein the heat exchanger is oriented such that lubricant in the refrigerant exits the heat exchanger through the output with the refrigerant.
 40. The temperature control system of claim 33 further comprising a fluid input for circulating a fluid through the heat exchanger, the fluid exchanging heat with the refrigerant.
 41. The temperature control system of claim 40 wherein the fluid is cooled by the heat exchanger.
 42. The temperature control system of claim 40 wherein the fluid comprises methyl nonafluoroisobutyl ether.
 43. The temperature control system of claim 40 wherein the fluid comprises methyl nonafluorobutyl ether.
 44. The temperature control system of claim 40 wherein the fluid is used to control temperature in the workpiece chuck.
 45. The temperature control system of claim 33 wherein the workpiece chuck is used to support a semiconductor wafer. 